Calendar Man is fascinated by dates and calendars – even his real name is a play on the Julian and Gregorian calendar. His crimes always have a relationship to the date that they are committed. The theme may be related to what day of the week it is or to a holiday or to a special anniversary on that date; he will plan his crime around that day. He often wears different costumes which correspond to the significance of the date, though he does have a main costume which has various numbers (meant to represent days on a calendar) sprouting from the shoulders.

After his first appearance, in which his crimes were based on the seasons of the year, his next appearance was in Batman #312 (June 1979), where his crimes were based on the days of the week, and his costumes reflected the Norse gods they were named for, along with Saturn. On Sunday he did not commit any robberies as it is a day of rest and he was planning to leave town. This issue also marked the first appearance of his most commonly known "calendar cape" costume. His next appearance in Batman #384-385 (June–July 1985), sees the Calendar Man at the onset of the Crisis being used as a pawn of the Monitor in an attempt to find someone to potentially eliminate the Batman for profit. In this instance, the Calendar Man's theme is holidays, and he attempts to use the young Jason Todd, as Robin, as the Batman's Achilles' heel with the promise of his demise on the first day of Spring, but it is ultimately Robin who is responsible for his defeat.

Because his crimes are generally petty and often ridiculous in nature, he is notorious among both heroes and villains alike for being something of a joke. Consequently, his post-Crisis appearances have been few and far between. He was once recruited by Killer Moth to form the villain team known as "The Misfits".